1. Technical Field of the Invention
This invention is related to hydroponic plant growth systems, and more specifically to growing plants in a hydroponic growth medium or substrate comprising activated carbon fibers.
2. State of the Prior Art
Hydroponics is a method of growing plants by providing mineral nutrients from mineral nutrient solutions to plant roots instead of from soil. In general, there are two main types of hydroponics—solution culture hydroponics and medium culture hydroponics. Solution culture hydroponics does not use a solid medium or substrate for the roots, whereas medium culture hydroponics includes a solid medium or substrate for the plant roots. Solid medium cultures are generally categorized by the type of solid medium used, which broadly includes sand culture, gravel culture, and rock wool culture. Typical media used for solid medium hydroponic cultures include the following: (i) Diahydro, which is natural sedimentary rock that comprises fossilized remains of diatoms; (ii) Expanded clay, which comprises clay pellets that are fired in kilns to expand into porous particles; (iii) Coir or coco peat, which is the leftover material after the fibers have been removed from the outermost shell of the coconut; (iv) Mineral wool, which includes fibers made from minerals or metal oxides, including fiberglass, ceramic fibers, and rock wool, also known as stone wool, which is an inert substrate made by spinning molten rock or lava into masses of fine, intertwined fibers; (v) Perlite, which is volcanic rock that has been superheated into very lightweight, expanded glass pebbles; (vi) Vermiculite, which is another mineral that has been superheated to expand it into light pebbles; (vii) Sand; (viii) Gravel; (ix) Brick shards; and (x) Polystyrene.
Of the examples listed above, mineral wool, and especially rock wool, is one of the most widely used solid media in hydroponics, especially in commercial hydroponic plant growing operations, because of its ability to hold water and a high percentage of air at the same time, and it provides a good mechanical structure to hold the plant stable. However, it does have a high pH, which is generally not suitable for plant growth, so it usually requires some acidic conditioning, and, while its water retention capabilities compare favorably to the other example hydroponic media listed above, it must still be watered frequently, if not continuously. Manufacturers of rock wool and other mineral wools have tried to address this problem by forming denser material, but such modifications inhibit root penetration. Also, mineral wool is prone to dusting, and the fine dust particles are small enough to lodge in people's lungs, which is harmful and can cause cancer and other diseases. Compositing materials, such as phenyl formaldehyde or furan resin, have been used in efforts to improve the tensegrity and reduce brittleness of mineral wool materials, but some of the composites are hydrophobic and have to be treated, such as by addition of mineral wetting agents or surfactants, in order to be useful as a hydroponic plant substrate. However, such wetting agents can leach out of the mineral wool material, which decreases the hydrophilic properties of the mineral wool substrates, and some of them may have toxic effects.
There are also environmental costs inherent in the use of mineral wools for hydroponic substrate materials. For example, raw materials for rock wool have to be mined, and the temperatures for the manufacture of rock wool exceed 1,600° C., which requires high energy input. Also, rock wool factories exude large quantities of smoke that contain air pollutants in nearly every category of toxins, including radioactive materials, carcinogenic substances, and heavy metals, and the process consumes vast amounts of water. Another problem is that mineral wools do not compost or biodegrade, and, after use, most of it is hauled to landfills for disposal, which adds to the environmental problems.